The cores of early UK graphite moderated research and production nuclear fission reactors operated at temperatures below 150°C. Due to this low temperature their core graphite contains significant amounts of stored (Wigner) energy that may be released by heating the graphite above the irradiation temperature. This exothermic behavior has lead to a number of decommissioning issues which are related to long term "safe-storage", reactor core dismantling, graphite waste packaging and the final disposal of this irradiated graphite waste. The release of stored energy can be modeled using kinetic models. These models rely on empirical data obtained either from graphite samples irradiated in Material Test Reactors (MTR) or data obtained from small samples obtained from the reactors themselves. Data from these experiments is used to derive activation energies and characteristic functions used in kinetic models. This present research involved the development of an understanding of the different grades of graphite, relating the accumulation of stored energy to reactor irradiation history and an investigation of historic stored energy data. The release of stored energy under various conditions applicable to decommissioning has been conducted using thermal analysis techniques such as Differential Scanning Calorimetry (DSC). Kinetic models were developed, validated and applied, suitable for the study of stored energy release in irradiated graphite components. A potentially valid method was developed, for determining the stored energy content of graphite components and the kinetics of energy release. Another parameter investigated in this study was dedicated in the simulation of irradiation damage using ion irradiation. Ion bombardment of small graphite samples is a convenient method of simulating fast neutron irradiation damage. In order to gain confidence that irradiation damage due to ion irradiation is a good model for neutron irradiation damage the properties and microstructure of various grades of ion irradiated nuclear graphite were also investigated. Raman Spectroscopy was employed to compare the effects of ion bombardment with the reported effects of neutron irradiation on the content of the defects. The changes of the of defect content with thermal annealing of the ion irradiated graphite have been compared with the annealing of neutron irradiated nuclear graphite.

With a birth prevalence of 1 in 1000, neural tube defects (NTD)s contribute considerably to morbidity and healthcare costs. Known genetic and environmental (non-inherited) risk factors for NTDs account for a small portion of risk, suggesting unidentified risk factors. In animal studies, maternal alcohol and pesticide exposures, independently, led to excess neural cell death, resulting in too few cells for neural tube closure. Human studies report no association between alcohol exposure and NTDs, but small to moderate positive associations for pesticide exposure. Such human etiologic studies of NTDs require a large base population, but frequently include only live births. Exclusion of cases by pregnancy outcomes may create ascertainment and response bias, complicating interpretation of findings. Using data from the National Birth Defects Prevention Study (NBDPS) and the Iowa Registry for Congenital and Inherited Disorders (IRCID), the independent effects of maternal periconceptional (1 month prior through 2 months postconception) alcohol and occupational pesticide exposure on the development of NTDs were examined, and differences in Iowa NTD cases were characterized by pregnancy outcome. Maternal reports of alcohol exposure were obtained for 1223 NTD case infants and 6807 control infants. Adjusted odds ratios, estimated using multivariate logistic regression, were near unity for NTDs by any maternal alcohol exposure, binge episode(s), and type(s) of alcohol consumed. Occupational pesticide exposure was assigned by industrial hygienists for mothers of 502 case and 2950 control infants. Adjusted odds ratios for any exposure and cumulative exposure to any pesticide, insecticides only, and insecticides + herbicides + fungicides were near unity for NTDs. Insecticide + herbicide exposure was positively associated with spina bifida. Among the 279 Iowa NTD case infants ascertained by the IRCID, 167 live births and 112 were other pregnancy outcomes (fetal deaths and elective terminations), which increased in proportion over time. Selected infant and maternal characteristics of live births and other pregnancy outcomes were similar. NBDPS eligibility varied significantly by pregnancy outcome, but participation rates did not. NTD case mothers were similar to Iowa NBDPS control mothers. Efforts were made to improve upon prior etiologic studies of these exposures and NTDs, including increased sample size and improved exposure specificity. Some exposure strata (e.g., herbicides only) and outcome strata (e.g., other rare subtypes) were limited by small numbers. All results may have been affected by response and ascertainment bias. Future studies should aim to use similarly detailed exposure classification methods, increase sample size in less prevalent NTD subtypes, and improve ascertainment of fetal deaths.

Thesis advisor: David Broido / We present fundamental studies of phonon and electron transport in semiconductors. First principles density functional theory (DFT) is combined with exact numerical solutions of the Boltzmann transport equation (BTE) for phonons and electrons to calculate various transport coefficients. The approach is used to determine the lattice thermal conductivity of three hexagonal polytypes of silicon carbide. The calculated results show excellent agreement with recent experiments. Next, using the infinite orders T-matrix approach, we calculate the effect of various neutral and charged substitution defects on the thermal conductivity of boron arsenide. Finally, we present a general coupled electron-phonon BTEs scheme designed to capture the mutual drag of the two interacting systems. By combining first principles calculations of anharmonic phonon interactions with phenomenological models of electron-phonon interactions, we apply our implementation of the coupled BTEs to calculate the thermal conductivity, mobility, Seebeck and Peltier coefficients of n-doped gallium arsenide. The measured low temperature enhancement in the Seebeck coefficient is captured using the solution of the fully coupled electron-phonon BTEs, while the uncoupled electron BTE fails to do so. This work gives insights into the fundamental nature of charge and heat transport in semiconductors and advances predictive ab initio computational approaches. We discuss possible extensions of our work. / Thesis (PhD) — Boston College, 2019. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Physics.

京都大学 / 0048 / 新制・課程博士 / 博士(農学) / 甲第22075号 / 農博第2367号 / 新制||農||1072(附属図書館) / 学位論文||R1||N5229(農学部図書室) / 京都大学大学院農学研究科地域環境科学専攻 / (主査)教授 近藤 直, 准教授 小川 雄一, 教授 清水 浩 / 学位規則第4条第1項該当 / Doctor of Agricultural Science / Kyoto University / DGAM

Fundamental advances in cathode materials are key to lowering the operating temperature of solid oxide fuel cells (SOFCs). Detailed understanding of the structural, electronic and defect formation characteristics are essential for rational design of cathode materials. In this thesis we employ first principles methods to study La(Mn/Co)O3 and LnBaCo2O5+δ (Ln = Pr, Gd; δ = 0.5, 1) as cathode for SOFCs. Specifically, factors affecting the O vacancy formation and migration are investigated. We demonstrate that for LaMnO3 the anisotropy effects often neglected at high operating temperatures become relevant when the temperature is lowered. We show that this fact has consequences for the material properties and can be further enhanced by strain and Sr doping. Tensile strain promotes both the O vacancy formation and migration in pristine and Sr doped LaMnO3, while Sr doping enhances the O vacancy formation but not the migration. The effect of A-site hole doping (Mg2+, Ca2+ or Ba2+) on the electronic and magnetic properties as well as the O vacancy formation and migration in LaCoO3 are studied. All three dopants are found to facilitate O vacancy formation. Substitution of La3+ with Ba2+/Mg2+ yields the lowest O vacancy formation energy for low/intermediate spin Co, implying that not only the structure, but also the spin state of Co is a key parameter. Only for low spin Co the ionic radius is correlated with the O migration barrier. Enhanced migration for intermediate spin Co is ascribed to the availability of additional space at the transition state. For LnBaCo2O5+δ we compare the O vacancy formation in GdBaCo2O5.5 (Pmmm symmetry) and GdBaCo2O6 (P4/mmm symmetry), and the influence of Sr doping. The O vacancy formation energy is demonstrated to be smaller in the already O deficient compound. This relation is maintained under Sr doping. It turns out that Sr doping can be utilized to significantly enhance the O vacancy formation in both compounds. The observed trends are explained on a microscopic level. Furthermore, we consider antisite defects as they may modify the electronic and O migration properties but are rarely studied in double perovskite oxides. It turns out that O vacancy formation is significantly easier in PrBaCo2O5.5 than in GdBaCo2O5.5, the difference in formation energy being hardly modified by antisite defects. Finally, having established that the O vacancy formation energy is significantly lower in PrBaCo2O5.5 than in GdBaCo2O5.5, we study the O Frenkel energy and migration of O ions in PrBa(Co/Fe)2O5.5. The electronic structure and charge redistribution during defect formation are analyzed. We demonstrate that Co↔Fe substitution strongly affects the formation of defects and, consequently, the O migration. The low O Frenkel energy points to a high concentration of O vacancies. The migration of the O ions shows a distinct anisotropy.

This dissertation main point is to take up with fotovoltanic cells metering methods. Dissertation work dwells with the most common defects rising during the fotovoltanic cells manufacturing. Also, there is a diagnosis workshop proposal and realisation. Workshop uses the Light Beam Inducted Voltages (LBIV) method. By the help of this method, fotovoltanic cells structures are analised and compared to the Light Beam Inducted Current (LBIC).

Master’s thesis deals with the optimalization of low-temperature cofired ceramic lamination process that affects the final quality of 3D structures (eg., channels, cavities, membranes, etc.). The paper evaluates the influence of lamination parameters (pressure, temperature, time) on the formation of defects in the structure, which were detected by appropriate methods. The last parts describes designed and simulation cooling water system using LTCC technology.

This diploma thesis handles with problems of reducing the production costs. The costs are connected with produce of scraps on Opel Delta project, where is the zero rework process booted. This work contains analysis of scraps for several periods and etablished actions to decrease inception of scraps.

This dissertation is the study about the future of solar power stations in the Czech Republic, describing the history, composition, principle of solar power stations and types of defects. Is primarily focuses on the future and recycling of solar power stations and solar panels. The conclusion of this disertation describes and evaluates own survey which is oriented on operators of the solar power stations.

The presence of cracks in rotors is one of the most dangerous defects of rotating machinery. This can lead to catastrophic failure of the shaft and long out-of-service periods. The occurrence of a crack in a rotating shaft introduces changes in flexibilities which alters the dynamics during operation. This research deals with detecting damage in rotors by means of constantly monitoring the variation in the rotor’s dynamics during normal operating conditions. This project entails a computer finite element section as well as an experimental investigation. The flexibility in the region of the crack is different from an uncracked section. A finite element model of a shaft is built and investigated. The damaged model is the same except that the nodes in the location of the crack are not equivalenced in order to represent the crack. A simple constant cross-sectional shaft with semi-circular transverse surface cracks varying in size have been modelled on the Patran finite element software and a normal modes analysis was done using the Nastran solver. The results revealed a change in the natural frequencies due to the variation in the size of the crack. The experimental investigation involved creating sample shafts with damage positioned in them that would closely resemble what one may find in actual real-life situations and the dynamics during rotation with various torsional loadings are investigated and monitored using three methods. A fibre-optical sensor, Digital image correlation system and telemetry strain gauges were used. Undersampling techniques were used for the DIC system. Results showed that the fibre-optic sensor is by far the most favourable as it is able to detect damage under constant operation. The finite element model was updated by re-modelling the geometry, damage and material properties. The solution of the analysis matched the experimental results closely and model verification was achieved. / Dissertation (MEng)--University of Pretoria, 2013. / Mechanical and Aeronautical Engineering / unrestricted